1. Field of the Invention
The present invention relates to device for mounting and positioning a tool holder to a tool rest such as turret of a machine tool.
2. Related Art
In order to work a workpiece at high precision by a machine tool such as lathe, it is necessary to accurately locate a tool holder with respect to a tool rest such as turret of a lathe. For this purpose, the tool rest of the machine tool is provided with a device for positioning the tool holder (tool holder positioning device).
That is, a seating surface is formed to the tool rest, and a plurality of recessed portions are formed to the seating surface. The tool holder is formed with a coupling surface so as to accord with the seating surface of the tool rest, and the coupling surface is formed with protruded portions so as to be fitted into the recessed portions formed to the tool rest. When the coupling surface of the tool holder abuts against the seating surface of the tool rest and the protruded portions of the coupling surface are fitted into the corresponding recessed portions, the tool holder can be positioned with respect to the tool rest.
In a conventional technology, in order to precisely position the tool holder and the tool rest, the recessed portions and the protruded portions are formed as key grooves and keys, respectively, and these key grooves and keys are formed such that a side surface at which the key contacts the key groove is perpendicular to that of the other key and key groove (for example, refer to Patent Publication 1: Japanese Patent Laid-open Publication No. 2006-167862). Furthermore, the protruded portion is attached to a front portion of a spring piece to position the tool holder on the tool rest, and at the time when the tool holder is fastened to the tool rest by means of screws, the spring piece is flexed (for example, refer Patent Publication 2: German Patent Application Laid-open Publication 102005045662).
In the positioning method using the key and key groove disclosed in the Patent Publication 1, a small gap is generated between side surfaces of the key and the key groove, and because of this reason, there may be a fear of causing a deviation such that the tool holder is not precisely positioned. This deviation is caused in an X-axis direction or a Y-axis direction, or in a twisting direction θ around a Z-axis in view of perpendicularly intersecting X-Y axes and Z-axis perpendicular to the X-Y axes on the seating surface and coupling surface.
Furthermore, a working for fitting the key into the key groove while abutting the coupling surface of the tool holder against the seating surface of the tool rest is troublesome, which results in that the key and the key groove may be easily damaged at the fitting time, thus proving a problem.
In the positioning method disclosed in the Patent Publication 2, when the tool holder is attached, the spring piece supporting the protruded portion in a cantilever manner is flexed, so that the axis of the protruded portion may be inclined, which is at first perpendicular to the coupling surface of the tool holder and the seating surface of the tool rest. Therefore, the positioning of the tool holder may not be precisely performed because of the twisting and contacting of the protruded portion and the recessed portion.